The present invention relates to a variable orifice for a pulverized coal pipe of a pulverizer installed to control a pulverized coal conveying speed and pressure of the pulverized coal pipe from the pulverizer of a thermal power plant to each boiler.
A thermal power plant that uses coal as a main material generates electricity by supplying finely powered pulverized coal together with air, burning the pulverized coal in a boiler, vaporizing water in a water pipe pumped into the boiler, and rotating a turbine.
Such a thermal power plant typically includes a pulverizer for pulverizing supplied coal into pulverized coal of a fine size and supplying the pulverized coal to a boiler through a pulverized coal pipe, a blower for supplying air through the pulverized coal pipe, and the boiler for burning a mixture of the pulverized coal and the air conveyed through the pulverized coal pipe.
In the above-mentioned thermal power plant, a pulverized coal pipe is connected from a pulverizer to each boiler in a branch manner so as to convey pulverized coal from one pulverizer to a plurality of boilers. Thus, because a conveying distance from the pulverizer to each boiler is different, it is necessary to control the pulverized coal conveying speed and pressure of the pulverized coal pipe connected to each boiler in order to equalize the injection pressure of the pulverized coal supplied to the boiler. To this end, an orifice is installed in the pulverized coal pipe of the pulverizer connected to each boiler.
FIG. 1 is a front view showing a general pulverizer. FIG. 2 is a plan view of an embodiment of FIG. 1. FIG. 3 is a perspective view showing an orifice for a pulverized coal pipe of a pulverizer according to the related art.
As shown in FIGS. 1 and 2, the pulverizer includes a frame 10, a coal supply pipe 20 connected to an upper portion of the frame 10 to supply coal into the frame 10, a coal grinder (not shown) installed inside the frame 10 to grind the supplied coal into pulverized coal, a plurality of pulverized coal pipes 30 connected to the upper portion of the frame 10 to supply the pulverized coal to respective boilers, and an orifice 40 connected to and installed on a pipeline of each of the pulverized coal pipes 30, reducing a cross-sectional area of the pipeline, and controlling the conveying speed and pressure of the pulverized coal.
In the pulverizer configured above, when the coal is introduced into the frame 10 through the coal supply pipe 20, the coal is grinded into the pulverized coal by the coal grinder installed in the frame 10. The pulverized coal is raised by air or gas supplied to the inside of the frame 10 with ascending air current and discharged to the pulverized coal pipe 30 and then supplied to each boiler. At this time, the conveying speed and pressure of the pulverized coal moving through the pulverized coal pipe 30 are controlled by the orifice 40 connected to and installed on the pipeline of each of the pulverized coal pipes 30.
As shown in FIG. 3, the orifice 40 according to the related art includes a pipe body 41 connected to and installed on a pipeline of a pulverized coal pipe for supplying pulverized coal from the pulverizer to a boiler, an enclosure 42 coupled along the outer circumferential surface of the pipe body 41, a pair of opening and closing plates 43 separated up and down inside of the enclosure 42 and slidably installed to face each other so as to reduce a cross sectional area of pipe body 41, and a rotary knob 44 for sliding the pair of opening and closing plates 43 to be close to or away from each other and reducing or expanding the cross sectional area of pipe body 41. Although not shown in the drawing, a power transmitting portion (not shown) is provided for converting a rotational movement of the rotary knob 44 into a linear movement of the pair of opening and closing plates 43. That is, when an operator rotates the rotary knob 44 in the forward direction, the pair of opening and closing plates 43 slides to be close to each other such that the cross sectional area of pipe body 41 is reduced and when the operator rotates the rotary knob 44 in a reverse direction, the pair of opening and closing plates 43 slides to be away from each other such that the cross sectional area of pipe body 41 is enlarged. Accordingly, the conveying speed and pressure of the pulverized coal passing through the orifice 40 are controlled.
However, in the conventional orifice 40 configured as described above, the pair of opening and closing plates 43 are slidably installed inside the enclosure 42. There is a fatal problem that since the pulverized coal continues to be pushed into the inside of the enclosure 42 while remaining on a surface of the opening and closing plates 43, the sliding operation of the opening and closing plates 43 itself becomes conventionally impossible by the accumulated pulverized coal.
In order to solve such a problem, in the ‘variable orifice for a pulverized coal pipe of a pulverizer’ of Korean Registration Patent Publication No. 10-1140463 filed and registered by the present applicant, by deviating from a slide-in method into the inside of the conventional enclosure of the opening and closing plates for controlling the conveying speed and pressure of the pulverized coal, as shown in FIGS. 4 and 5, a new hemispherical opening and closing system for opening and closing a hemispherical tube 43c while rotating and operating a pair of inner opening and closing plate 43a and outer opening and closing plate 43b having a curved shape in mutually different directions so as to reduce or expand the cross-sectional area of the pipe body 41 is configured, thereby fundamentally preventing the orifice from malfunctioning or being inoperable due to the pulverized coal accumulated inside of the conventional enclosure.
In the hemispherical opening and closing method as described above, the inner opening and closing plate 43a and outer opening and the closing plate 43b are formed of high strength carbon steel. As shown in FIG. 5, since high pressure air passes along with the pulverized coal, abrasion of an inner circumferential surface actively proceeds by the impact of pulverized coal particles due to fast flow. In particular, erosion (C) occurs in upper end portions of the inner opening and closing plate 43a and the outer opening and closing plate 43b which face each other due to abrupt abrasion, which causes a problem in the conveying speed and pressure control of the fine pulverized coal.
The eroded upper end portions of the inner opening and closing plate 43a and the outer opening and closing plate 43b are formed in an unspecified shape, and when each is replaced with a whole, since it costs a lot, the inner opening and closing plate 43a and the outer opening and closing plate 43b are reused through a repair of cutting only the eroded parts into a specific shape separately and manufacturing a piece in accordance with the cut shape by welding. Time and cost-consuming maintenance for repairing the inner opening and closing plate 43a and the outer opening and closing plate 43b are also problematic.
As shown in FIGS. 4 and 5, in the case of the variable orifice for the pulverized coal pipe of the pulverizer according to the related art, a fixed rib 43d and the hemispherical tube 43c are installed inside of the pipe body 41 having the same diameter as that of the pulverized coal pipe 30, and the inner opening and closing plate 43a and the outer opening and closing plate 43b are coupled to each other through the hemispherical tube 43c, which causes a problem that a conveyance amount of the pulverized coal conveyed through the pipe body 41 is lowered, and, in particular, the pulverized coal is stacked and accumulated in a space between the hemispherical tube 43c and the pipe body 41.
Furthermore, as shown in FIG. 4, the configurations of a rotation motor 45 for rotating and opening and closing the inner opening and closing plate 43a and the outer opening and closing plate 43b and a gear portion 46 for transmitting the rotational force of the rotation motor 45 are designed coaxially with an inner rotation shaft 46a, which causes a problem that the length is increased and the space usability is lowered during installation.